1. Field of the Invention
This invention relates to cellular mobile communications and more especially, a technology for providing multiplicity through allocating time slots by having time divisions for multiple terminals.
2. Description of Related Art
For cellular mobile communications, time division multiplexing involves multiple terminals differentiated for each time period being allocated a time slot thereby enabling multiple terminals to be employed. A problem results when transmitting from multiple different neighboring base stations at the same time however, because as there is a close distance between receiving terminals there is a great degree of interference occurring through transmission from a nearby base station to a terminal.
As shown in FIG. 7 for example, as transmission is occurring simultaneously from base station 1 to terminal A and from base station 2 to terminal B because there is a very short distance between terminal A and terminal B there is a great degree of interference occurring from base station 1 to terminal B and from base station 2 to terminal A.
A conventional method for solving this kind of problem is to have transmission from only one base station or a method whereby closely located multiple base stations transmit to only one terminal. The time scheduling method in “Simple Inter-Cell Coordination Schemes for a High Speed CDMA Packet Downlink” Proceedings of VTC 2000 Spring, Feb. 9, 2002 will now be described with reference to FIGS. 8 and 9.
In FIG. 8 only base station 1 is transmitting and base station 2 does not transmit at the same time, therefore there is no interference directed at terminal A. In FIG. 9 both base station 1 and base station 2 transmit to terminal A. In addition to eliminating interference for terminal A this achieves a diversity effect.
Thus with the conventional time scheduling scheme described, when a terminal is located in a boundary region of respective cells of neighboring base stations transmission can only be performed from one neighboring base station or neighboring base stations can only transmit the same signal to one terminal.
The above problem means that a base station needs time slots when it can be used or carriers are restricted. This leads to an inefficient rate of terminal access.